Posted
by
Soulskill
on Saturday June 21, 2014 @04:50PM
from the make-like-a-tree-and-get-outta-here dept.

An anonymous reader writes: Years of research has gone into products that are hydrophobic — they resist getting wet. But nature solved this problem long ago, and it's ubiquitous outside our buildings and homes. You've probably seen it yourself, after a light rain: water collects in round droplets on many leaves from trees and plants, refusing to spread out evenly across the surface. This article explains why that happens using super slow-mo cameras and an electron microscope. "[T]he water isn't really sitting on the surface. A superhydrophobic surface is a little like a bed of nails. The nails touch the water, but there are gaps in between them. So there's fewer points of contact, which means the surface can't tug on the water as much, and so the drop stays round. ... [After looking at a leaf in the electron microscope,] we saw this field of tiny wax needles, each needle just a few microns in length! The water drops are suspended on these ultra-microscopic wax needles, and that keeps it from wetting the surface."

Garden Mythbusters: Does Sunlight and Water Mixing Really Burn Leaves?
Two years ago, four Hungarian scientists published a paper called “Optics of sunlit water drops on leaves: conditions under which sunburn is possible” in the journal New Phytologist. Given the near-universal belief that water drops can scorch plant leaves on a sunny day (e.g. the RHS book How To Garden: “Under a hot midday sun, water droplets on leaves will act as miniature magnifying glasses and may scorch them”), you may be surprised — or you may not — that no one had previously checked to see if this actually happens.
First of all, the short answer is no.
Are there any circumstances under which water drops on leaves can cause sunburn? Yes, but only if the leaf has a dense covering of water-repellent hairs, in which case drops can be held above the leaf surface, allowing them to focus light on the surface itself.

I'm curious how this might happen. As the sunlight passed through the water droplet, wouldn't the water heat up, expand and change as a result losing the magnifying effect? Even if the light passing through didn't do it, sitting right next to the supposed burning surface would. Anyways, the heat can only get so hot and the water will evaporate.

It just doesn't seem possible to me. Now, I know they say watering your lawn or garden in the mid day heat is stressful on the plants, but I was under the impression

It's not much but not all water droplets magnify light due to surface tension and positioning of the droplets on less than smooth surfaces. So if it does happen to be one that would magnify light, the slight expansion would change the surface tension dynamics to some degree and thereby changing the shape of the droplet.

This isn't about water growing in volume to some major size, it's about changing it's shape because it only acts like a concentrated magnifying glass when it has certain shapes present.

This will also depend upon the location of the light source. Overhead? No burn, most likely. 45 or 135 degrees? It's possible, depending upon the level of photon flux being concentrated onto a small spot, assuming the water droplet is even the correct size to project a clean focused on the surface of the leaf, given distance.

assuming the water droplet is even the correct size to project a clean focused on the surface of the leaf, given distance.

That's where I think the major problem would be. As the water heats, changes within it's shape would/should occur. I don't think it could stay focused long enough to harm the plants. I know water on a windshield usually diffracts and reflects light making somewhat less pass through.

Garden Mythbusters: Does Sunlight and Water Mixing Really Burn Leaves?

Two years ago, four Hungarian scientists published a paper called “Optics of sunlit water drops on leaves: conditions under which sunburn is possible” in the journal New Phytologist. Given the near-universal belief that water drops can scorch plant leaves on a sunny day (e.g. the RHS book How To Garden: “Under a hot midday sun, water droplets on leaves will act as miniature magnifying glasses and may scorch them”), you may be surprised — or you may not — that no one had previously checked to see if this actually happens.

First of all, the short answer is no.

Are there any circumstances under which water drops on leaves can cause sunburn? Yes, but only if the leaf has a dense covering of water-repellent hairs, in which case drops can be held above the leaf surface, allowing them to focus light on the surface itself.

The point is moot.This question became a "Thing" mostly because of people growing pot in their basements. About 15yrs ago it became something you could do with nothing more than a trip to Home Depot. Unfortunately, due to draconian laws people are forced to hide this to the point the plants are usually grown in secret rooms, fake cabinents, etc... So the plant is in a very tight area, lots of humidity and questionable airflow. Because of this situation, watering became because of all the bending and manuver

Uh, no. It's been a "thing" as long as I can remember, and I started gardening in 1965. Vegetables, not pot.

Camellias (the kind they sell at Home Depot, that make showy flowers) DO die back if they get water on the leaves in sunlight. Why I have no idea, but I lost several that way.

As to the "bed of nails" -- when I was a kid I observed that if I rubbed a finger across the leaf surface, water would stop beading up, and the leaf would get wet. Well, now I know why -- I was crushing these microstructures. And

There are only two things in life that you should ever be completely certain about:1 - You are NOT allowed to talk about it.2 - You are not permitted in any way to ever talk or communicate in any other method, about it.

You do not need to know what new features the iPhone 6 has, you simply need to know that you need to buy it. If you dont buy it, you should feel very, very bad about yourself. You will then be required to spend a considerable amount of time internally r

Why would a plant evolve a method that cleans the under-side of its leaves?

Come on, man, THINK for a second. What *else* might stick to leaves that the plant might not want? What about fungal spores? You know, organisms that might *eat* you if you were a tree? If you thought about it for a second, deciduousness in itself is a scheme to battle fungi too.

This really is "missing the forest for the trees" or in this case, leaves.

Why would a plant evolve a method that cleans the under-side of its leaves?

Come on, man, THINK for a second. What *else* might stick to leaves that the plant might not want? What about fungal spores? You know, organisms that might *eat* you if you were a tree? If you thought about it for a second, deciduousness in itself is a scheme to battle fungi too.

This really is "missing the forest for the trees" or in this case, leaves.

--BMO

Your poast is relying wholly on the assumption that water repelling abilities work the same way on microscopic spores as on macroscopic water droplets.You may need to revisit this assumption.

If you thought about it for a second, deciduousness in itself is a scheme to battle fungi too.

I think you might be thinking too hard. Water conservation in colder climes/drought conditions is the most often mentioned advantage of flora shedding their leaves. I've never heard "battling fungi" mentioned as an advantage for "deciduousness" until now.
http://en.wikipedia.org/wiki/D... [wikipedia.org]

Yeah, but then the leaves are around its stem or trunk, which is an even less-good place to get a fungal infection. Leaves can be shed; roots and trunks cannot.

Deaves dry up before being shed (as water and nutrients are sucked out of them) and this generally applies to infected leaves as well, at any time of year. (Fall is not typically when fungal infections happen; rather, where spring rains and summer heat overlap.)

A bit of fun for those involved, but funnily enough plant science has actually investigated this over many decades. Go to a search engine of your choice and look up "waxy cuticle" and "trichomes". Sorry if I appear snide, but this is rather like someone posting an article about how they were amazed at what is inside their desktop PC, with photos and everything, as if no one had looked inside one previously. Neither the word cuticle nor the word trichome appear in that article, which shows they made no attempt to find out anything about their subject. Nice videos though, would be good for teaching!

True, this is nothing novel, but IT does incorporate cool electron microscope pictures and sweet slow motion video set to music, so It must be high tech.

on the other hand, Its odd that this subject came up, because it instantly reminded me of this:
http://www.realclearscience.co... [realclearscience.com] Because my first thought when I read the headline was "because they are fuzzy on a tiny scale"
I know that the wax needles are a shade smaller than the 13 nanometers of amplitude that the researchers in the article I linked di